1. Field of the Invention
The present invention generally relates to a method, medium, and apparatus for reserving resources when a handover occurs in a mobile network. More particularly, the present invention pertains to a method, medium, and apparatus for reserving resources by searching for a candidate access router and a candidate crossover router for an area where a mobile node will potentially move, and pre-reserve or re-reserve the appropriate resources through a router found through the search.
2. Description of the Related Art
As information and globalization ages draw near, research into active wireless Internet systems has increased. Wireless Internet can be briefly classified into fixed wireless Internet and mobile wireless Internet. Fixed wireless Internet is limited in mobility, but has superior transmission capacity and speed. Systems for WLAN (Wireless Local Area Network), B-WLL (Broadband Wireless Local Loop), LMDS (Local Multipoint Distribution Service), and Bluetooth, belong to the wireless fixed Internet. By contrast, the mobile wireless Internet, which is implemented by different types of systems in notebook computers and PCs, according to the generations of the mobile communication network, secures the mobility superiority, but is limited in transmission capacity and speed.
With the development of mobile communication networks, the mobile wireless Internet has developed from an initial form, such as CDPD (Cellular Digital Packet Data) using the 1st generation AMPS (Advanced Mobile Phone Service) network, to a service form using wireless application protocols such as WAP (Wireless Application Protocol), ME (Mobile Explorer) and I-mode, based on the 2nd or 2.5-generation IS-95/GSM network. The standardization of ALL IP mobile networks based on IMT-2000, which is the 3rd-generation mobile communication system, has progressed in stages, and it is expected that the IP-based standardization will be gradually carried out from the fields of IP-based core networks to wireless access networks and terminals.
The present ALL IP mobile network is the next-generation mobile communication network which has become a matter of great concern all over the world, with standardization work having progressed in the 3GPP (3rd Generation Partnership Project) around Northern Europe and in the 3GPP2 (3rd Generation Partnership Project 2) around North America. From these projects, many technical issues have been brought to light in the academic world, through various kinds of forums and through the standardization and development of the ALL IP mobile network carried out through various kinds of consortiums made up by world-famous mobile communication network providers, manufacturers developing network constituent elements, Internet service providers providing new Internet services, and manufacturers of IP packet network constituent elements.
In order to support the mobility in the mobile wireless network where the ALL IP is implemented, an MIP (Mobile IP) and a QoS (Quality of Service), securing a reliable transmission of data and multimedia traffic, are required. The reliable transmission of the multimedia traffic is supported by a pre-reservation of network resources, for which an RSVP (Resource Reservation Protocol) has been mainly used. However, since the present RSVP was not designed to take into consideration the mobility of wireless networks, a proper resource reservation cannot be made when MIP is implemented.
After the appearance of MIP, research for a resource reservation for mobile networks has continuously progressed, and the representative protocols are MRSVP (Mobile RSVP), RSVP-MP (RSVP Mobility Proxy), and CORP (method of Concatenation and Optimization for resource Reservation Path).
FIG. 1 illustrates paths for pre-establishing resources, according to the conventional MRSVP. MRSVP classifies resource reservation states into a passive reservation state and an active reservation state. The passive reservation state is a state where a resource has been previously reserved, and not presently in use, and the active reservation state is a state where the reserved resource is in use. A proxy agent is provided in an access router to manage the transmission of a user's mobile terminal or mobile node 10 from the passive reservation state to the active reservation state. The mobile node can move within a mobile network and accordingly changes its network access position. The proxy agent manages cells adjacent to a cell where the mobile node is positioned, and preemptively takes part in a multicast RSVP session through special reservation schemes, wherein traffic is not actually transferred.
Referring to FIG. 1, the mobile node 10 establishes a communication session with a correspondent node 20 through a path 1. The correspondent node 20 communicates with the mobile node 10 by connecting with the access router CAR included in a core network.
In this state, if a handover of the mobile node 10 occurs, the mobile node 10 transmits a specification message to adjacent access routers AR2, AR3, . . . , and ARn. The specification message includes a flow specification, which is to be transmitted to a remote proxy agent by the mobile node and a flow ID (Identification). Between the access routers AR2, AR3, . . . , and ARn, where a communication session is not currently established, and the correspondent node 20, the passive reservation state is set. If the mobile node 10 moves, it can extend the reservation path by changing a corresponding passive reservation state to an active reservation state and by transferring traffic through the active reservation state.
Although this solved the problem of time delay of the QoS re-establishment, MRSVP pre-reserves resources of adjacent cells where the mobile terminal may move in the mobile network, which may be short of resources, thereby wasting resources in the access network. The mobile node should keep a mobility specification that includes position information for all of the neighbors of the mobile node while the mobile node moves and as it establishes a communication session with the correspondent node 20. Since an intermediate router manages all state information about passive reservation states, unnecessary overhead occurs, which emphasizes a corresponding problem of the mobile network having limited scalability. When the mobile node 10 moves, communication sessions between mobile node 10 and previous resources in a previous cell are not promptly released, thereby creating a double reservation being kept with respect to the same communication session, causing a waste of resources. As these handovers frequently occur, generating such double resource reservations, the resource availability of new communication sessions becomes disturbed.
FIG. 2 illustrates paths for establishing new resources through an address changing method, according to the conventional RSVP-MP. The RSVP-MP structure is mutually combined with hierarchical mobility management schemes of MIP, is provided with an RSVP-MP agent placed at MAP (Mobility Anchor Point) or in GFA (Gateway Foreign Agent), and performs an address change between an LCoA (Local Care-of-Address), which is an address of the access router, and an RCoA (Regional Care-of-Address), which is a global address of another address.
Referring to FIG. 2, the mobile node 10 establishes a communication session with a correspondent node 20 through path 1. If the mobile node 10 performs a handover from an area managed by AR1, which is currently connected to the mobile node 10, to an area managed by AR2, mobility 10 is allocated with CoA, a new temporary address, and requests a re-establishment of resource reservation according to the change of paths. If an end-to-end re-establishment of resources from the mobile node 10 to the correspondent node 20 is made, the resource re-establishment creates a time delay, preventing the mobile node 10 from being properly provided with QoS.
However, if the handover of the mobile terminal 10 occurs, the RSVP-MP structure performs communication by converting LCoA of the access network into RCoA that is a global address through an MP (Mobility Proxy) and using RCoA. Thus, according to the RSVP-MP structure, re-establishment of entire paths is not required, but only requires the path in a section between AR1 and MAP, in which LCoA is used, to be re-established. That is, RCoA is used from MAP to the correspondent node 20, and thus, even if a handover occurs, it is not required to re-establish the RSVP session from MAP to the correspondent node, but only requires the RSVP session to be re-established between the mobile node to MAP. Since RSVP-MP does not require the re-establishment of the end-to-end resource reservation, it can reduce time delays due to the limited required re-establishment of the RSVP-MP session.
Although RSVP-MP does not require the reestablishment of the end-to-end resource reservation, a time delay of as much as one round-trip time still occurs in order to establish the resource reservation, and a prompt release of the reservation state of the resources established through the old access router is not performed, thereby similarly again causing the double reservation of resources. If the handover frequently occurs, the handover still disturbs the resource use for new communication sessions due to the double resource maintenance. Since the RSVP-MP structure should be implemented in parallel to the hierarchical mobility management schemes of MIP, which have not yet been completed, it cannot be an independent protocol and, accordingly, may be changed as it is implemented.
FIG. 3 is a view illustrating a conventional CORP type RSVP path extending process through a hierarchical reservation path and path extending process using an optimized reservation path.
Referring to FIG. 3, the CORP type RSVP provides QoS by using a method of extending the existing RSVP path if a handover occurs. The CORP type RSVP uses a CRP (Concatenation for Reservation Path)r to extend the RSVP path.
The CRP type RSVP extends the RSVP path using PRPs (Pseudo Reservation Paths). The CRP type RSVP determines one representative BS (Base Station) among BSs (Base Stations) managed by one access router, and pre-reserves the resources for adjacent BSs.
Referring to FIG. 3, several access routers AR1, AR2, . . . , ARn, which belong to the access network, manage respective areas area 1 to area n. Each respective area includes several cells, and a BS manages the respective cells. If the mobile node 10 performs a handover in the area managed by one access router, the BS that manages the cell that the mobile node 10 accordingly has reached, transmits a CRP information message (that is, information message) for informing BSs, of the adjacent cells, of the arrival of the mobile node at BSs, and makes the adjacent cells pre-reserve their resources.
The continuous extension of the RSVP path by CRP makes an infinite path or a loop path, and in order to prevent this, an ORP (Optimization for Reservation Path) is used along with CORP. Specifically, if a handover occurs within an area managed by one access router AR1, the handover is processed according to CRP, while if a handover occurs due to the mobile node's movement to another access router AR2, the mobile node 10 establishes a new RSVP session with the correspondent node 20. Accordingly, in the case of the handover occurring in one access router, resources can be promptly secured, and thus previous problems caused by the path extension can be solved with QoS being secured.
As described above, since CORP pre-reserves the resources of adjacent cells to which the mobile node will move and simultaneously establishes the end-to-end RSVP session in a mobile network having insufficient resources, the inefficient waste of resources occurs in the access network. Since CORP uses a multicast method when establishing a new session by extending the path, and since there should also be a new RSVP session established from a new access router to the correspondent node 20 whenever the mobile node moves to another access router, trouble occurs in scalability of the network. Although CORP releases old resources, unlike MRSVP, the release of the existing resources according to CORP includes the release of the existing resources up to the correspondent node 20, and thus a prompt process is not achieved and a new session establishments for other terminals are disturbed.